For interior trim members of automobiles, a soft vinyl chloride resin has been widely used in the past. Since the soft vinyl chloride resin is excellent in molding processability into parts and is relatively inexpensive, it has been used much for interior trim skin materials of instrument panels, doors, ceilings and the like, handle materials, lever knobs, various grips, etc. In recent years, however, there has been pointed out a possibility that the vinyl chloride resin becomes a cause of a poisonous gas when incinerated, so that replacement of the soft vinyl chloride resin used for the above parts with materials other than the soft vinyl chloride resin has been studied.
Particularly for the automobile interior trim parts, an olefin-based thermoplastic elastomer is most widely used as a substitute for the soft vinyl chloride resin. The olefin-based thermoplastic elastomer is a material excellent in various points such that it is lightweight, is excellent in moldability and processability into parts, can be readily recycled and generates no poisonous gas during combustion, but on the other hand, it has a disadvantage of poor scratch resistance.
On this account, the olefin-based thermoplastic elastomer has not been used as it is for the parts requiring scratch resistance, and in the actual circumstances, an elastomer having been improved in scratch resistance by subjecting it to surface treatment or the like is employed (see, for example, patent document 1).
As the olefin-based thermoplastic elastomer having been improved in scratch resistance, a composition obtained by adding a hydrogenation product of a styrene/isoprene block copolymer having a large quantity of 3,4-bonds of polyisoprene block moieties to a crosslinked olefin-based thermoplastic elastomer containing polypropylene and EPDM as basic components and prepared by dynamic crosslinking has been proposed (see, for example, patent document 2). The hydrogenation product, however, not only has tackiness but also is expensive as compared with the soft vinyl chloride resin that has been mainly used in the past, and hence, use of the composition is restricted in the actual circumstances.
Further, a composition having been improved in scratch resistance by adding polybutene to the above-mentioned crosslinked olefin-based thermoplastic elastomer has been proposed (see, for example, patent document 3). This composition is superior to the general-purpose crosslinked olefin-based thermoplastic elastomer in scratch resistance, but actually, it is inferior in appearance to the soft vinyl chloride resin that has been used in the past.
Under such circumstances as above, the present inventors have found that compositions of a propylene/ethylene copolymer having a syndiotactic structure, a propylene/butene/ethylene copolymer having the same structure and a polyolefin resin are very excellent in scratch resistance and abrasion resistance, and by combining them with an appropriate lubricant, etc., they exhibit scratch resistance and abrasion resistance comparable to those of the soft vinyl chloride resin (see, for example, patent documents 4 and 5). These compositions, however, are inferior in heat aging resistance, and the gloss varies in the aging test of 100° C. and about 24 hours, so that it is difficult to use them for automobiles.    Patent document 1: Japanese Patent Publication No. 070742/1991    Patent document 2: Japanese Patent Laid-Open Publication No. 053789/1995    Patent document 3: Japanese Patent No. 2904708    Patent document 4: pamphlet of International Publication No. 2005/053951    Patent document 5: pamphlet of International Publication No. 2005/103141